Known aerated edible products include meringues. They are produced by cooking an aerated egg-white mixture. The air bubbles in the mixture do not expand during cooking.
Known aerated snack products are generally vegetable (e.g., potato) or fruit-based. They tend either to be very dry and brittle or to have a greasy texture.
Aerated vegetable or fruit-based snack products are usually formed by extruding material of a dough-like consistency, in order to set up internal shear forces which cause the dough to become plastic, so enabling it to expand on heating. The plastic mass is then subjected to high temperatures, to convert water in the mass to steam. The steam generates hollows which, when the heat treated mass is dried, fill with air which results in a product having a puffed structure. Doughs used in such processes have a low moisture content, usually not exceeding 10%, otherwise shear forces will not be set up within the dough when it is extruded and it will not become plastic. No moisture is added to the plastic mass after extrusion because, if it is not viscous enough when heated, steam will escape from, rather than form hollows within the plasticised mass, with the result that it will collapse and will not form a puffed structure.
Steam may be generated by the use of cooker-extruders or microwave ovens in the case of dry products, or by frying the plastic mass in oil or fat, in the latter case, the product has a greasy texture. However, it is difficult to obtain defined and regular product shapes by using these techniques and often the product has uneven aeration.
Steam generated by these techniques requires high temperatures or long time periods. Such techniques result in the breakdown or removal of volatile materials such as the isoprenoids which are widely used as flavourings. Consequently, known aerated snack products are given topical coatings or dustings which are commonly fastened to the product by a fat wash. The resulting flavoured product has a high fat content, and the fat and powders can be transferred to the fingers during consumption. In addition, such products suffer from poorly flavoured centres.